The Sentai-based Hitotsu-kis hosts share elements with their respective series.
Kishiryu-ki is formed from a table tennis champion. Table tennis was the last thing the Ryusoulgers did with Nada before his death.
Ressha-ki is formed from Taro's boss Sanae, who wishes for youth. The ToQGers themselves were young children artificially aged up due to the events of the series.
Kaitou-ki is formed from a deliveryman known only as Kurokuma, who resorts to stealing light fixtures from houses and is theorized by Shinichi to have snapped due to the stresses of the job. The Lupinrangers became Phantom Thieves due to trauma in their lives as well.
Chouriki-ki is formed from an onigiri chef named Mizuno. Onigiri are vaguely shaped like pyramids, which were a recurring motif in Ohranger.
Keisatsu-ki is formed from a police detective named Sayama, whose obsession with pursuing justice led to his transformation. Keiichiro from LuPat was known for his near-fanatical pursuit of the Lupinrangers.
Doubutsu-ki is formed from a nurse named Fuka Kirita, whose desire is for everyone to be cared for. Like Yamato and his father, she works at a hospital.
Chikyuu-ki is formed from the principal of Tsunokaku High School. The Fivemen were a Sibling Team of teachers.
Mashin-ki is formed from an artist named Sakaki. Juuru aka KiramaiRed was likewise an artist who liked to draw on his sketch pad.
Tokumei-ki is formed from the childlike spirit of an old man named Taichi Izawa. Masato aka Beet Buster was similarly an avatar in the real world while his body was trapped in subspace, while Tokumei-ki's Super-Speed is a homage to Red Buster. His insistence for playing "red light green light" (where the players have to stand still whenever the seeker is looking at them) is also an homage to Hiromu's freezing up. Not to mention that his lack of a proper childhood also references the fact that Hiromu and Yoko trained themselves against Vaglass at the cost of a normal life when they were seven and three years old.
Kaizoku-ki is formed from an avid manga fan who seeks to steal talent to make his own manga, just as pirates are wont to do. The fact that he targets mangaka seems to be a nod to digital piracy as well, in a reference to manga being scanned illegally to be read by fans without paying.
It's also a nod to Twokaizer, who was such a fan of manga that he looted Mangatopia to read all the good manga he could.
It could also be interpreted as how many doujin manga artists "steal" the ideas of other (and usually famous) manga artists as either influence in their own works or to study the production.
Can be also a reference to the world-famous magazine knwon as Shonen Jump, who has a pirate's head as their logo.
Shuriken-ki is formed from a ninjutsu practitioner named Minoru Ohno, which is of course a reference to the Igasaki family being a family of ninjas. This also serves as the reason why Shuriken-ki was able to give even Don Momotaro trouble one-on-one since unlike the other Hitotsu-kis, its host's desire was explicidly to become a stronger fighter.
Uchuu-ki is formed from an idol fanboy. His habit of collecting idols can be likened to collecting stars, and Kyuranger did have a celestial motif with one of their allies being a radio show personality. Not to mention the fact that he does the dancing theme hip thrusts after becoming Uchuu-King and screaming "GALAXY!".
Zyuden-ki is formed from an attention-seeking widow. The Kyoryuger roll call invited onlookers to be amazed at their transformation, and Zyuden-ki also uses samba rhythms while fighting in a manner similar to how the team dances during their Transformation Sequence.
Kousoku-ki is formed from a shōgi player who is in high school. The Turborangers were high school students as well, and his Super-Speed calls back to the Turborangers having this power in crossovers that they didn't have in their original series.
Gekisou-ki was created after his wife was hospitalised by motorcyclists. The Carrangers’ enemies were a biker gang.
Kyoryu-ki is a gamer who's trying to beat an RPG, while Zyuranger was itself inspired by fantasy RPGs.
Choujin-ki is formed from a woman involved in a Love Triangle and who's fallen for the Black Ranger, in a clear nod to Jetman's own.
Engine-ki is formed from the ghost of a young woman similar to the main villain trio of Go-Onger coming back as ghosts in their VS movie with Shinkenger.
On top of that, the place the ghost is trapped in is a Telephone booth, referencing the Changers of the core three Go-Ongers, the phone-shaped Go-Phones.
Adding on to that is the belief that ghosts are the souls of deceased people, referencing the ‘Soul’ theme of the Go-Ongers’ collectibles, the Engine Souls.
Ninpuu-ki is formed from Kuroiwa, the director of New First Love Hero's In-Universe movie adaptation. The Hurricanegers had a theater/kabuki submotif. Not to mention that he's played by Kuwaga Raiger's actor himself.
Gosei-ki is formed from a martial artist seeking worthy opponents. The Dairangers were a team focused on Chinese martial arts. Like with Shuriken-ki, his desire to seek stronger opponents means that Don Momotaro struggled to defeat him until Zenkaizer Black stepped in.
Samurai-ki is formed from Shirai, one of Shinichi's predecessors as Saru Brother. The Shinkengers were themselves Legacy Characters, passing down their power from one generation to the next.
Denji-ki is formed from Goda, the owner of an IT company. The Megarangers were a team explicitly based on cutting-edge technology.
Juken-ki is formed from Tamaru, a student studying the Japanese Constitution. It's not readily apparent, but his motivation forms a pun; "exam-taking" is homophonous with Juken, and "[the] Constitution" is homophonous with Kenpo, both of which were key terms in Gekiranger.
It's also fitting that he's the Hitotsu-Ki/King that Don Doragoku and Torabolt face for the debut of their Robotaro forms and Toradragonjin, as they are based on Chinese culture.
Ninja-ki is formed from Koichiro Higashi, a young man hiding from his estranged mother. The Kakurangers were of course ninja, for whom hiding is an art form.
Dai-ki is formed from an older man who wants to recruit better employees. Professor Hideki Hongō was looking for suitable people to become the Goggle Five.
Mahou-ki is formed from Minoru Ohno, the same host as Shuriken-ki. This refers to Yakumo from Ninninger, who was a magic user, and was taught by Tsubasa Ozu from Magiranger.
Kagaku-ki is formed from Mizuho Iijuin, a woman who wanted to acquire a painting important to her. Not only is her form based on a science experiment, her explosive desire for art can be said to match the explosions associated with the Dynamen.
Bakuryuu-ki is formed from Nagai, a company president known to rampage to the point of bullying his employees. "Rampage" can be translated into Japanese as abare, as in Abaranger (and amusingly enough, Avataro). Moreover, his power is super speed, which is the civilian power of Dino Thunder Red, and of course Power Rangers: Dino Thunder is an adaptation of Abaranger.
Choushinsei-ki is formed from Koyama, a man addicted to spicy food. Spicy food is often described with explosive terms, analogous to a supernova (which is what choushinsei translates to).
Tensou-ki is shown to possess multiple hosts. The Goseigers faced multiple villain factions such as the Warstar, the Yuumajuu, and the Matrintis, before fighting the fallen angel Brajira.
GoGo-ki is Minoru Ohno's third go-around as a Hitotsu-ki. Aside from mimicking BoukenRed, Boukenger was the series that followed Magiranger. Boukenger was also an anniversary series celebrating Sentai that came before it. It also ties to how Magine and Vroon from Zenkaiger, who are homages to those two series, default to combining together.
Taiyou-ki is formed from Tsuyoshi again (as well as Shinichi and Haruka briefly). Their colors (pink, blue, yellow) loosely correspond to the Sun Vulcan members (with pink in place of red), and Sun Vulcan preceded Donbrothers as a sequel series (to Denziman and Zenkaiger respectively). Not to mention that Sun Vulcan is the only known Sentai to have a permanent replacement of their Red Ranger, reflecting to how Sonoi considered himself the new leader now that he's defeated Taro.
Tokusou-Ki is formed from an oden stand owner who didn't want his customers to be judgemental over his cooking.
Choujuu-Ki is formed from a young scientist, and the Livemen (as well as their rivals at Volt) were young scientists. His desperation of wanting to understand what youth is mirrors Gou Omura's backstory as a child prodigy who was forced to undergo a harsh study regimen and wasn't allowed to have fun with his peers. Meanwhile, his gun attacks as hitotsu-king is a clear nod to Dr. Mazenda's arsenal.
Kyukyu-Ki is formed from a man seeking to be rescued from strange events around him. GoGoV, of course, was a Sentai that rescued the common people from dangerous situations.
Seijuu-Ki was about to make Minoru Ohno its host before Sonoza transferred it to Sonoshi instead. Hyūga was the appointed Ginga Red before he was forced to pass it on to his brother Ryōma.
Denshi-Ki absorbs Tsubasa/Inu Brother as one of her victims. The Denziman's mentor, a dog, sacrificed himself to essentially become an integrated circuit in the Denziman's sole mech.
Ja-Ki is formed in the same episode as the debut of Don Killer and Don Killer Killer, who are killer androids. JAKQ, on the other hand, was a team of cyborgs.
Mirai-Ki is formed from a driving instructor, calling back to the time Ayase/TimeBlue had to re-apply for a driver's license since his future one wasn't accepted.
Hikari-Ki is formed from Santa Claus himself. Both Santa and Buddha (who serves as the inspiration for Hikari-Ki and an icon in the Maskman base) are important mythological figures.
Himitsu-Ki is formed from Tsutomu Kameda, a scammer (as in, someone who secretly works to swindle others) who wanted to escape from a sinister family. Of course, a team of secret agents like the Gorengers could help him easily. Alternately, the Donbrothers are the secret agents in this episode, as they don disguises and make up stories about themselves to fool Tsutomu.
Moreover, the story takes place during the new year in-universe, as in the first day of the year. Of course the Gorengers are the first Sentai.
Choudenshi-Ki is formed from a praise-starved office worker named Rikio Ono. His boss resembles Doctor Man, while he himself resembles Monster, The Brute of Bioman's Quirky Miniboss Squad. His work proposal and multi-colored tie also evoke the Biomen themselves.
Hyakujuu-Ki is formed from Tsuyoshi yet again. His previous stints as a Hitotsu-Ki were as Taiyou-Ki (referencing the fifth Sentai) and as Gekisou-Ki (referencing the twentieth Sentai). Gaoranger was the twenty-fifth Sentai. Not to mention that his persistence in searching for Miho echoes back to GaoBlue and GaoBlack having the motto "never give up", only done for a more sinister purpose.
Dengeki-Ki is formed from Tamaki, the former host of Ja-Ki. Both JAKQ and Changeman have the word "dengeki" (lit. electric shock) in their titles.note Though the word is used in different contexts for both series.
Sekai-Ki is formed from Shinnosuke, Tamaki's partner whose desire is for her to return to normal. Battle Fever J was the series that followed JAKQ and resumed Sentai after a year's hiatus. Shinnosuke himself is also Tamaki's boyfriend, aka "BF", which is also the initial used by the Battle Fevers.
Ohsama-Ki is formed from Minoru Ohno in his fourth stint as a Hitotsu-ki. The King-Ohgers have royal connections, as did Bouken Yellow. Given that the Overseers had a hand in his creation and his motif, one could consider him to be their attempt at a Puppet King.
It's also thematically fitting for Ohsama-ki to be the final Sentai-based Hitotsu-ki to appear in the show; the very first, Kishiryu-ki, was themed on knights, who were typically dubbed by monarchs.
Haruka mistaking Sonoi and Sonoza for Taro Momoi could be seen as a reference to Super Sentai fans who prefer stoic badass Reds over the Hot-Blooded Reds the franchise has been known for as of late.
The Donbrothers' civilian identities and their Sentai forms are basically polar opposites of each other:
Taro is an unassuming-looking delivery courier who is Beneath Notice at first glance. He's a showy, hammy fighter as DonMomotaro.
Shinichi is a slender, intelligent poet. As SaruBrother, he's the burly muscle of the team.
Haruka is a high school student who's inexperienced in combat. As OniSister, she fights with a big club like how high school delinquents are often depicted with a baseball bat.
Tsubasa is a standoffish loner implicated in a crime. InuBrother is based on a dog, which are generally considered to be loyal and are used by law enforcement.
Tsuyoshi is an ordinary Salaryman. As KijiBrother, his extreme height and status as the first full-time male Pink in the franchise makes him stand out.
The very next episode has Haruka being uncharacteristically cooperative and helpful, going to help Tsubasa despite clearly not wanting to, praising Shinichi's "genius" ideas and even trying to comfort Tsubasa by pretending to be his presumed lover. Which seems odd at first until you realize Haruka saw how much better the Donbrothers were with the much nicer and helpful Marina and she's might have genuinely realized her attitude was a problem and/or is trying to honor Marina by trying to play a similar role. Of course Haruka being Haruka her personality isn't quite up to the task as shown by her instinctive reaction to Tsubasa trying to embrace her when hallucinating was to slap him and her losing her temper at Tsubasa and nearly beating his head in with a weight when he rejected her "comfort".
Jiro has a rather unusual personality for a Sixth Ranger, being enthusiastic, jumping at the call, and being much more of a team member than Taro was. That's because Jiro and Taro have the archetypal personalities for their respective team positions reversed; Taro being a One-Man Army who isn't a good team player is the kind of personality one would associate with the Sixth Ranger instead, while Jiro acts more like a typical Red.
#15 reveals that Jiro, unlike the other Donbrothers not named Taro, isn't part of the Kibi-Points system. This may be due to him being from the Noto world like Taro is, rather than being a regular human like the others.
The challenge in #18 is to strike Taro once, with the prize being to be viewed as Taro's equal. Now look at his interactions with Sonoi and how chill he is with him over his own companions and remember how Sonoi once struck down Taro.
Haruka rather bluntly tells Taro his beloved pet beetle from childhood is definitely dead, as they don't live a year let alone over a decade. Rather harsh truth, but Taro has been telling such brutal truths all show because he can't lie and doesn't see the point in doing so even to spare people's feelings. Taro's either rubbing off on her, or she deliberately did so because she's following Taro's own principles and assumes he also wants to hear the honest truth instead of lies to spare his feelings. And Taro despite clearly being hurt doesn't seem to have a problem with Haruka doing so, presumably because he either expects such brutal honesty given to him in return especially from someone who knows him well or realizes he'd be a hypocrite to get upset over something he does to other people constantly and accepted a taste of his own medicine.
Another possibility is that seeing Taro acts not like his usual self hurt Haruka the most, and she does have strong feelings for him (as evidenced when she was even willing to sacrifice her life so Taro would live again even if for a moment), so she opted to tell the harsh truth knowing he could take it and that this decision would be for his own good.
Hanamura's unexpected return to trying to get back with Haruka in #19 seems odd when it ended so badly and decisively last time he showed up. But that was in the Marina timeline which only Haruka (and Kaito but it's not like he's privy to Haruka's love life nor would he care) remembers. As far as he knows Haruka went from desperately wanting him back to suddenly wanting nothing to do with him.
Many Sentai Sixth Rangers tended to work separately from the main team because they preferred to work alone. Jiro is an inversion: He wants to join the Donbrothers, but his multiple issues including being a terrible team player and a Superpowered Evil Side means that the team doesn't want him to join them.
Why did the Donbrothers Avatar Change into the Fivemen when fighting Denji-ki? Because the former are based on teachers while the Megarangers were students themselves.
Why is Tsubasa the seeming arch-rival for "Sayama" the Cat Juto? Aside from the latter possibly remembering his life as a police officer and Tsubasa being a fugitive, there's also the fact that Tsubasa has a dog motif while "Sayama" has a cat motif.
If one considers the fact that the Donbrothers who hang out at Donbura the most are Taro (Red), Shinichi (Blue), Haruka (Yellow), and Tsuyoshi (Pink), then you can see that combined with Kaito they pretty much correspond to the Zenkaigers. It helps that both Blues are the smart muscles of their group and the Pinks have some sort of flying ability.
In episode 25, how can Tsubasa get a job when his wanted status is still active? Probably because the café that hired him is so desperate to stay in business that they're willing to take anyone in, even wanted criminals.
Another very likely possibility is that he used his connections to disguise his appearance some and impressed them with his culinary skills, as it manages to impress even Momoi Taro so much that he recovered from his exhaustion instantly just to approve.
The Reveal concerning the origins of the Jūto recontextualizes the Don Clan's overthrow by the Nōto Council. Instead of an innocent royal family being overthrown by extremist revolutionaries, it instead implies that the Don Clan had gone a step too far and therefore had to be overthrown by the Well-Intentioned Extremist Council. Similarly, Don Murasame is implied to be a weapon designed by the Council to deal with the Jūto, yet was freed before he was supposed to do so by Mother.
Part of Taro's revival involves using others' energy and essence to provide him with the necessary stamina, which mirrors some of how Sonoi himself was revived: the draining happened while they were having an eating contest, which prevented them from feeling exhaustion or from noticing that they were being drained, and it also involved using a weapon (the Geartlinger) to drain it; meanwhile for Sonoi's revival Taro had been offered a banquet before the last rites to provide him with enough energy that would be drained via the Zanglassword into Sonoi's hollowed armor.
The reason the Noto cuisine is tasteless and looks like cotton candy is explained by two facts: one is that it is meant to provide sustenance, and the other is that trying to give it any flavor or form would mean sacrificing practicality in consumption and possibly reduce the number of nutrients it should provide.
After having their essences drained to be fed to Taro so he could be revived, it's very easy to see whose essence belongs to who: Pink for Tsuyoshi, white for Sononi, orange for Sonoza, yellow for Haruka, blue for Shinichi, and red for Sonoi. The last one might seem off, until you remember that Sonoi's color would be blue under natural circumstances (confusing with Shinichi's) and that he has been revived with what amount to buckets of Taro's essence, which is red.
This tweet explains how the Noto trio somehow manage to learn each other's curiosities. To explain:
Sonoi expresses interest in wanting to know about art. Throughout the series, he ends up experiencing love (or rather a deep mutual bond) with Tarou, which is what Sononi wants to learn.
Sononi expresses interest in wanting to know about love. Throughout the series, by putting herself out for people to get baited into talking to her, plus her interactions with Tsubasa, she ends up interacting the most with other people and seeing their emotions, which is what Sonoza wants to learn.
Sonoza expresses interest in wanting to know about human interactions and emotions. At some point in the series, he manages to grab a copy of Haruka's manga First Love Hero and wanting to read more of it, and in turn helps Haruka in creating art, which is what Sonoi wants to learn.
Why does Taro Avatar Change into GolDon ToQ #1 to fight Choujuu-Ki? Because Choujuu-Ki's powers involve weaponizing youthful energy, and the ToQgers are/were literal kids, so one could assume that allowed Taro to No-Sell the attacks.
Similarly, Taro Avatar Changes into GolDon Akaninger against Himitsu-Ki because Gorenger and Ninninger share the distinction of being the two teams whose members are designated by their Japanese color name, instead of their English color name (e.g. Akarenger and Akaninger vs, say, ShinkenRed or HurricaneRed).
Minoru somehow being alive despite his third Hitotsu-ki form being slain by Sonoi may seem odd until you realize that at the time Sonoi was ressurected and empowered by Taro's energy, which may have also accidentally given him the power to return a Hitotsu-ki back into a human instead of truly killing them off like the Donbrothers have shown.
For the longest time we had no idea what happens to people consumed by a monster, that somehow gets released after the monster is destroyed, but #38 clears that up: after Denshiki eats both Tsubasa and the head chef, Tsubasa explains that they are in a pocket dimension inside the Hitotsuki.
While they assume Don Killer and Don-Killer Killer looks like Taro and Shinichi for aesthetic purposes, it takes some thinking back to when Shinichi challenged Taro to a tongue-twister: they are both so good at it that their match would potentially never end.
A Bread, Eggs, Breaded Eggs situation arises in a rather meta manner. The first time a Jūto was defeated for good was at the hands of Don Murasame, showing his true purpose as a Jūto killer. The second time was at Tsubasa's hands, showing that a Jūto can be defeated if its host is taken outside of the Forest of Slumbers. The third time is Jūto!Sayama getting defeated by Tsubasa wielding the Ninjarksword, thus combining the two situations.
Naoki Shiina being revealed to be Haruka from the future sheds light on a number of things:
How could Haruka perfectly plagiarize someone she never knew? Simple: her future self already knew what she wanted to create and so happened to make it before her present self.
There's no way someone can copy someone else's special recipe or cooking down to the exact taste, unless they were the same person.
At the end of New First Love Hero, the only person to actually like the movie is none other than Naoki Shiina. Of course she would, her present self is playing a leading role in the manga she wrote.
Why doesn't Tsuyoshi turn into a Hitotsu-Ki upon seeing Miho get hurt in #44? Aside from the possibility that one Hitotsu-Ki can only be active at a time (Choudenshi-Ki being active around this time), there's also the fact that this time, Tsuyoshi's anger and worry is justified, given that Tsubasa had the intention of killing the Crane Jūto and even successfully wounded her.
Plus this time he was neither under Hitotsu-Ki possession nor was forcibly possessed by one.
Jiro's adoptive father having the Don-killer-killer summon button was at first seen as a Contrived Coincidence at best, but now that it was revealed that he was a Penguin Jūto copying a Don Clan member it suddenly makes sense as why he had such thing on first place.
Why is the penguin both a symbol of the Don Clan and the highest rank of the Jūto? It's probably a reference to the fact that there are two species of penguin with suitably royal names, the king penguin and the emperor penguin.
Jiro's friends being skeptic and doubtful of his dreams of heroisms could come his father's attempt to keep Jiro in the village as his successor. Only for them to become more supportive once he actually left in order to lure him back in.
Tsubasa has been oft-compared to Gai/Black Condor from Jetman. He's a Black Ranger who ends up with Sononi, who is themed on Condorman.
Kaito being Zenkaiser Black makes a whole lot of sense as being implied to be the actual Kaito, as black is the color that absorbs all color. In other words, embodying all of Super Sentai up to that point.
Meanwhile, Don Momotaro turning white in Kaito's discussion during the final episode makes a lot of sense when you think about how white is a color that reflects all color, mirroring how Taro's role was to be the perfect foil for which the other Donbrothers improved themselves on.
The dishes that the Donburies team have their colors in them, though it requires some creative thinking to get there.
Tekkadon is topped with tuna sashimi which is colored red.
Tendon is spelled with the character for "heaven" (天), which evokes the imagery of a blue sky.
Katsudon contains yellow egg yolks.
Kaisendon is typically served with nori that can be seen either as black or dark green.
Gyudon is topped with red pickled ginger, which is more accurately colored pink.
Does Jin realize how much damage he's causing by forcing people to become a Super Sentai? Haruka is a 17 year old girl who has never had to fight for her life, and now has to leave a prestigious academy, loses her boyfriend and school and only has to rely on his words for the smallest chances of her ass being saved. And given how hand's off and cryptic he's been...
To say nothing of the implication that Tsubasa was framed for a crime in order to get him to join. How much of his life was ruined by this and his constant run to escape the law?
Also making things more horrifying is that the situations of the Donbrothers' civilian lifes could possibly even get worse since as Haruka notes in episode 3 even if she managed to write another manga, there is a possibility that she would once again be accused with plagiarism. Not to mention the fact that that something awful could happen to Shinichi or Tsuyoshi especially since the latter's greatest source of happiness in his dull and average life is his wife, who in the worst case scenario may get Stuffed in the Fridge or divorce him.
Episode 11 reveals Miho is a Crane Bestial, and one of the three Bestials that Jin warned the Noto Layer of. That begs the question as to when she became a Bestial, and if she has been one since before the start of the series. Another question is whether it's part of Tsuyoshi's misfortune.
At different points it is revealed that the "bad luck" came to them in different ways: Tsubasa was challenged to never talk about what he saw for one whole year by who is implied to be the leader of the Juto before he became Inu Brother, Tsuyoshi has always been unlucky even before becoming Kiji Brother, and Shinichi's bad luck didn't impact his life in a meaningful way as it simply came, caused his house to be hit by a sudden localized earthquake once and that all light fixtures to be stolen, and then nothing bad ever happened again. This makes Haruka the odd one off.
In fact if you think about it nothing really changed for Tsuyoshi and Shinichi, and Tsubasa's "bad luck" hit him long before he became a Donbrother. Only Haruka was hit with horrific life changing misfortune after becoming one, which leads one to wonder if it's not something else going on with her, especially when the staff frequently mentions that she's the "Oni" who not really supposed to be on Momotaro's side according to the story.
Come episode #33 and Sonoi reveals the truth behind the powers of the Donbrothers: a product of the former Noto Royal family, the Don Clan, and it was supposed to activate after Taro fully awakened so that they could assist him. That implies, if not outright confirms, that Jin had no involvement whatsoever.
Tsuyoshi only cares about Miho's wellbeing till the point he outright helps the Noto Layer kill the Hitotsu-ki if they harmed her in any way. This makes you wonder if he has any family members left or if he has a bad relation with them.
Episode 10 explores the question of what happens when one of the Donbrothers quits via spending their Kibi Points. Not only do they return to their normal lives, the world also pulls in a Suspiciously Similar Substitute to ensure Don Momotaro always has companions of some sort, who are given a similar backstory that they may or may not handle as well as the originals. One wonders if Shinichi or Tsuyoshi replaced or could be replaced by someone who couldn't handle the Blessed with Suck inherent to being a Donbrother.
Not to mention the implication that this could happen at any moment, it might have even happened before the series began.
Given that the Kibi Point system still recognized Haruka and not Marina when Haruka undid the wish that would suggest that the Haruka is the "true" Oni Sister and Marina was just wish granted fill in. Which would suggest that all the current members are the original members.
Confirmed in Episode 21 where the previous Sarubrother shows up. However, it's played with in that he was never officially a Donbrother; he lost the powers due to using them for personal gain instead of fighting Hitotsuki. It's even mentioned that there were actually about 5000 other previous candidates who were rejected from the team for similar reasons.
Episode 19 features a ghost girl, of whom the only people that can see her without holding their breath are Taro and Kaito (who are Ambiguously Human), Tsubasa (who was infected by the Cat Juuto and survived) and Haruka. Why can Haruka see her? Even the ghost seemed surprised.
One possible theory is that Haruka did come close to dying when she used her Kibi Points to (temporarily) "revive" Taro, and that left her in a condition similar to Tsubasa.
Episode 23 has Tsubasa cursed into becoming a dog due to accidentally falling into an informal roadside shrine to a dog after being sent flying by the Hitotsuki. If not for Miho restoring the dog shrine and unwittingly lifting the curse in the process, Tsubasa would've lived the rest of his life as a normal dog, with no memories of his human life or even a sense of identity and, not having any meaningful connections with known relatives or even his fellow Donbrothers, the person known as Tsubasa Inuzuka would be eventually forgotten, leaving behind only a wanted poster.
The fact that Minoru Ohno, formerly Shuriken-Ki, came back as another Hitotsu-Ki as Mahou-Ki and then as GoGo-Ki implies that a person's desires can be so strong that the Donbrothers defeating them once isn't a guarantee they'll be okay. Not only is it entirely possible that people like Tsuyoshi can backslide and become Hitotsu-Ki again, it also shows that the Nōto's method of putting them in a dimensional prison is not without merit.
Predictably, Tsuyoshi does backslide into a Hitotsu-Ki when in #33 Sonoi forces him, Shinichi and Haruka to confront their greed and all three turns into Taiyo-Ki on the spot, with the later two reverting out of their own will as soon as they see Taro revived and only Tsuyoshi going into a rampage. Of course, he later apologizes for losing control (again) when Taro saves him.
The reveal that Hitoshi Hanamura's mother is a Juto brings three concerning thoughts to table: First is when she was replaced, second is whether or not she has been aware of Haruka's status as a Donbrother, and the third is whatever happened to Hitoshi.
Sonoi (and possibly the other Noto Generals) can force people's desire to overwhelm them and turn them into Hitotsu-Ki on the spot.
Jiro has shown numerous signs that he might be a Juto, and those includes:
Feral Jiro speaks in a raspy growl that mirrors that of Cat Juto when they finally chose to talk.
Feral Jiro is the original personality, who created a different personality to help him mingle, like the Crane Juto becoming Miho.
Even with the jossing, this creates a Fridge Horror when looking at ToraDoraJin in how the Tiger Robotaro is caged by the Dragon Robotaro.
He is highly susceptible to the Ninjark Sword, the only weapon that can harm or kill the Juto so far, to the point of being bedridden from the pain.
And now in #39 he appears in the end of the episode folding a penguin origami, implying or outright confirming him as the strongest Juto.
#45 deconfirms Jiro's Jūto status, but also confirms that the real Penguin Jūto in question was planning to turn him into one anyway.
Sonoshi can summon Anoni to fight for them, just like the Hitotsu-Ki. Couple that with the fact that Hitotsu-Ki normally can't possess a Noto and it is possible to assume that the Hitotsu-Ki are Noto or Anoni who have gone rogue.
Given that Don Murasame kills off Jūto for good and presumably takes down their hosts as well, one can only think of what Tsubasa's reaction would be once he learns of this, as well as the fact that Sononi deceived him by saying it's the only way he can save Natsumi. Not to mention that there's the potential of him doing so while Tsuyoshi is Forced to Watch.
Despite it being their first task, none of the Donbrothers have actually met or known Taro Momoi as a civilian, as with Tsuyoshi's civilian interaction with him implying they aren't aware of each other being comrades.
Tsubasa/Inu Brother is implied to have been co-orperating with Don Momotaro for a while now, and despite his worse social standing he doesn't seem at all at a rush to find "Taro Momoi" as a person nor did he recognise him when they met in-person, compared to Haruka who assumes she needs to find him personally. This implies the "swear allegience to Taro Momoi" task might have only required just acknowledging that Don Momotaro is a "Taro Momoi" to work with him and doesn't require knowing "Taro" personally.
There are implications that there are people higher than the Noto Layer in the chain of command, as evidenced by the existence of the Admin (Kaito) and how Jin has to tell even Sonoi that the visiting hours are over.
Episode 45 establishes, or at least heavily implies, that the inhabitants of Jiro's village, including Rumi and his other childhood friends, are all illusions created by the Penguin Juto. But we've seen scenes of Jiro's friends interacting with each other when Jiro isn't around. In Episode 20 in particular, we cut back to the village and see Rumi talking to her mother.
Given the Penguin Juto has the ability to create illusions, who is to say he didn't create an illusion for the viewers as well, just to keep us all in the dark as well?
At first it's possible to assume the Noto seals the Hitotsu-Ki to stop their reampage, but considering how Terasaki phrases his disgust at his own original kin, and what happens when a person is possessed by a Hitotsu-Ki, the answer for all might as well be simpler than that: The Hitotsu-Ki produces a massive amount of brain waves, which would sustain the Noto well, so they are "purged" (read: sealed in another dimension) to act like super batteries until they expire of natural causes.
Additionally, any victim of the Hitotsu-Ki adds to the energy they get per Hitotsu-Ki, making for a very tempting "Capture one and get a bunch free!" deal for the Noto.
The reveal of Taro's memories resetting and him becoming a blank slate is accompanied with Don Momotaro's colors fading out into a monochrome, nondifferent from that of Kaito as Zenkaiger Black, leaving a heavy implication that Kaito is the original Kaito, and that this has also happened to him in the past, so he is familiar with what is going on with Taro.
tweet explains how the Noto trio somehow manage to learn each other's curiosities. To explain: